The vaccine also didn't need an adjuvant, a substance added to a vaccine to make it stronger. There have been safety concerns about adjuvants.
Researchers were also able to use a whole virus, thought to produce better immunity responses, without any major side effects.
"We had been concerned with the idea that whole viruses have more side effects, but this doesn't show that," said Dr. Marc Siegel, an associate professor of medicine at New York University School of Medicine, and author of Bird Flu: Everything You Need to Know About the Next Pandemic.
CELVAPAN was tested on 275 adults aged 18 to 45, all of whom received two doses 21 days apart. Not only did the vaccine produce an immune response against the A/Vietnam/1203/2004 virus strain, but also against two related strains.
With all the successes demonstrated here, experts still point to some caveats. One is that the vaccine was only tested in younger adults (up to 45 years of age), not older adults where it would be most needed.
"We don't know how older adults would respond in terms of antibody levels," Imperato said. "We know that younger adults tend to form antibodies to influenza vaccines much better than older adults."
Having to give two doses is also a drawback. "As soon as you have to give two doses of a vaccine, even if it's not at a very long interval, it presents a problem with public compliance," Imperato said.
And there are many who believe bird flu will not result in a major threat to humans. "I still think there's no reason to believe that a virus that's so pathogenic to birds is automatically going to become pathogenic to humans," Siegel said. "In fact, most pandemics come from low-pathogenic viruses. We've got to watch this carefully, because it's such a killer [mortality rate is upwards of 60 percent in humans], but that doesn't mean by any stretch of imagination that i
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